A common way of producing molded thermoplastic articles known in the prior art is to heat thermoplastic polymers in a mold. For example, U.S. Pat. No. 4,382,757 discloses the molding of polystyrene beads in a patented apparatus through the introduction of steam into a mold. The steam heats the beads and causes them to expand and coalesce into a solid block of material.
Another method of heating thermoplastic materials to form molded plastic articles is disclosed in U.S. Pat. No. 4,840,758. This process involves mixing a radio frequency energy sensitizing agent comprised of N-ethyl toluene sulfonamide with a thermoplastic polymer. This mixture is placed in a mold and subjected to radio frequency energy for a time sufficient to heat the mixture. The mixture is then compressed to form the final molded product.
The prior art also discloses methods of compression molding a plastic article without the use of heat. In U.S. Pat. No. 4,108,940, a process for producing flexible molded articles is described. This process involves the compression of elastomers, such as carboxyl terminated polybutadiene, to produce an uncured, flexible product.
The use of organic solvents to treat thermoplastic articles in various ways is known in the prior art as well. Organic solvents have been used, for example, to reflow thermoplastic surfaces such as paint, as disclosed in U.S. Pat. No. 3,729,331. Solvents such as methylethylketone have also been used to treat polystyrene film in order to produce synthetic paper.
Notwithstanding the foregoing, there remains a need for a method of molding a plastic, such as polystyrene, to produce a relatively rigid product in a relatively short time without the necessity of heat.